This house is fine as long as he is a smallish syrian can be a cramped house for a large syrian. I think you are right to change the house unless varnished it can get a bit manky.
Try a plastic house and see how it goes, you can always go back after.
Alternatively try moving the house and putting a litter tray where your hammy is currently weeing as they may continue to go there once the house is moved
Good luck x